The human eye in its simplest terms functions to provide vision by transmitting and refracting light through a clear outer portion called the cornea, and further focusing the image by way of the lens onto the retina at the back of the eye. The quality of the focused image depends on many factors including the size, shape and length of the eye, and the shape and transparency of the cornea and lens.
When trauma, age or disease cause the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. The treatment for this condition is surgical removal of the lens and implantation of an artificial lens or IOL.
While early IOLs were made from hard plastic, such as polymethylmethacrylate (PMMA), soft, foldable IOLs made from silicone, soft acrylics and hydrogels have become increasingly popular because of the ability to fold or roll these soft lenses and insert them through a smaller incision. Several methods of rolling or folding the lenses are used. One popular method is an injector cartridge that folds the lenses and provides a relatively small diameter lumen through which the lens may be pushed into the eye, usually by a soft tip plunger. The most commonly used injector cartridge design is illustrated in U.S. Pat. No. 4,681,102 (Bartell), and includes a split, longitudinally hinged cartridge. Similar designs are illustrated in U.S. Pat. Nos. 5,494,484 and 5,499,987 (Feingold) and 5,616,148 and 5,620,450 (Eagles, et al.). In an attempt to avoid the claims of U.S. Pat. No. 4,681,102, several solid cartridges have been investigated, see for example U.S. Pat. No. 5,275,604 (Rheinish, et al.) and 5,653,715 (Reich, et al.).
These prior art devices used plungers that were substantially symmetrical about a longitudinal axis and generally contained a cylindrical or flared soft tip that completely filled the bore of the injector cartridge. See, for example, U.S. Pat. Nos. 4,681,102 (Bartell) and 4,919,130 (Stoy, et al.), and WIPO Publication No. WO 96/29956, the entire contents of which are incorporated herein by reference. Other plungers had hooked or forked tips meant to grasp the edge of the IOL. See for example, U.S. Pat. Nos. 4,573,998 (Mazzocco), 5,494,484 and 5,499,484 (Feingold), 5,616,148 and 5,620,450 (Eagles, et al.) and 5,653,715 (Reich, et al.), the entire contents of which are incorporated herein by reference. One plunger tip recently commercially introduced is designed so that the IOL rolls around the tip as the IOL is advanced down the cartridge. See U.S. Pat. No. 5,735,858 (Makker, et al.), the entire contents of which is incorporated herein by reference.
While these symmetric plunger tip designs work well with robust, rubbery, elastic lens materials, the performance of these tip designs is less than optimal when used with a viscoelastic material, such as a soft acrylic. In particular, the tip design that encourages the IOL to roll around the tip as the tip is advanced down the cartridge bore significantly increases the chances of damage to soft acrylic IOLs. The inventors have also discovered that viscoelastic IOL materials tend to flow around the plunger tip, regardless of tip design, and prior art tips do not address this material property adequately. Accordingly, a need continues to exist for an IOL injector plunger designed to optimize performance when used with a viscoelastic material.